Abstract: A data processing system with a dataset multiplexer that enables applications to be written to specify access to datasets as operations on logical datasets. During execution of an application by the data processing system, operations that access a dataset are implemented by accessing an entry in a dataset catalog for the logical dataset. That entry includes information to access the physical data source storing the logical dataset, including conversion of data from the format of the physical data source to the format of the logical dataset. An entry in the catalog may be created based on registration of a data source with the dataset multiplexer and may be updated automatically based on changes in storage of the dataset. This maintenance of the catalog may be partially or totally automated such that the system automatically adjusts to any changes in storage of the dataset without need for modification of any application.